Turn backs = People who fled back to Mexico, away from approaching U.S. agents along the border

Known Illegal Immigrants = Determined by counting the “got aways,” those who escaped and were tracked by cameras — or footprints — before they disappeared heading north.

Example:

U.S. Government Accountability Office

In comparison to 2006, the agency was being more effective.

Rebecca Gambler is the acting Homeland Security auditor for the Government Accountability Office. Gambler said eight of the nine southwest border sectors increased their effectiveness rates, most by about 20 percent.

But Gambler is also careful to note that each of the nine different sectors gather their data on "got aways" and turn backs differently.

“The rate cannot be compared across sectors,” she said.

Does this equation work?

Questions about the effectiveness of the U.S. Border Patrol have been the source of federal audits, Congressional hearings and just plain talk all along the border. The questions go back more than a decade.

In 2004, Tucson Sector Chief David Aguilar (now the deputy Customs and Border Protection commissioner) was among the first to talk about gaining “operational control of the border,” using a pointer and maps of the Mexican state of Sonora to point out where along the border the Border Patrol had been effective and where the agency needed to increase its effectiveness.